Ionization has long been used to promote the removal of particulate matter from air. In an early U.S. Pat. No. 945,917 to Cottrell (1910) particulate-laden air is ionized and the charged particles thereby formed were collected on an electrically grounded surface.
Precipitator-type air filters of the type depicted in U.S. Pat. No. 2,593,869 to Fruth (1952) first ionize the particulate-carrying air, and then pass the air flow between oppositely charged parallel plates to which the particulates adhere. Such precipitating air cleaners are highly efficient when the plates are initially clean. However, performance drops off as the plates become covered with collected dust. Hence regular cleaning is required to maintain efficiency. This cleaning operation for precipitator-type air cleaners is awkward and costly to effect.
It is known to also trap airborne particles in disposable filter media such as granulated charcoal and fibrous matrices of glass wool and the like. The trapping capacity of such filter media can be enhanced by ionizing the air, and dust therein, before it enters the filter medium. U.S. Pat. Nos. 3,706,182 to Sargent (1972) and 4,244,710 to Burger (1981) both depict such an arrangement.
In both of these references ions are introduced into the air flow stream by ion emitters positioned at an upstream location in the air flow, at a spaced distance from the filter medium that is intended to remove ionized particles. A prior invention that also relies on the upstream release of ions into air ducts has been made by the present inventor, as represented in U.S. Pat. No. 5,518,531.
Apart from whether ionization is present, it is known that the trapping efficiency of a trapping medium of dielectric material such as glass can be enhanced by polarizing the medium under an electrical potential field having a high field gradient.
Two examples of prior art patents based on the polarization principle are U.S. Pat. Nos. 4,549,887 and No. 4,828,586, the contents of which are adopted herein by reference. The first patent describes a pair of outer hinged screens for enclosing a pair of glass fibre pads in a kind of a "sandwich" with a central grid located therebetween. The central grid, made of coarse wire mesh that is on the order of 0.5 millimeters in diameter, is charged to around 7000 volts and the outer screens are grounded. The spacing between the charged screens is between two and five centimeters, producing an electric field gradient. This field gradient polarizes the non-conducting glass fibres rendering them more active in trapping dust particles, and more effective than non-polarized pads. This configuration does not generate ions to any significant extent.
An advantage of this polarized type of filter is that the accumulated dust is readily removed by exchanging the dust-laden fibre pads for fresh pads. However, polarized filter air cleaners are not as efficient as precipitator-type ionizing air cleaners. Considerable advantages can be achieved by combining features of both systems.
U.S. Pat. No. 5,403,383 to Jaisinghani depicts an "Ionizing Field Electrically Enhanced Filter" wherein air passes through ionizing wires before reaching a separately-spaced pad of dielectric material that has a grounded electrode on its downstream side. To effect increased ionization Jaisinghani provides a further charged "control grid" positioned upstream from the ionizing wires in the air flow. This control grid helps provide field gradients that will create the desired degree of ionization at the ionizing wires. However, this upstream control grid acts as an obstructing screen which limits the upstream diffusion of ions into the arriving air flow. Filter replacement does not disturb the ionizing wires which are separated from the filters and are permanently connected to the external supporting body of the overall system.
The present inventor has also obtained a U.S. Pat. No. 5,573,577 issuing after the priority date herein for an improved grid for use in a polarizing filter that is made of a fibrous conducting filament with many protruding filament ends. These pointed ends create ionization in the air passing through the polarized trapping medium, enhancing filter efficiency.
A major concern in respect of all ionization-based air cleaners is to minimize the production of ozone. Ozone is offensive to some and can be injurious above certain levels. Any system that relies on ionization should also minimize the production of ozone.
The production of ozone is associated with power consumption i.e. the providing of a current flow under an applied voltage potential. The design and fabrication of high voltage supplies that deliver significant current is complex and costly. Great advantages arise when high voltage supplies are operated at low power levels. By avoiding the production of corona and associated ozone, the advantages using a low power, high voltage supply become available.
Canadian Patent No. 1,294,226 discloses a low cost, low power, high voltage power supply that can be conveniently attached to a disposable air filter.
It is an object of this invention to provide for the incorporation of ionization into an air filtration system in a manner than is of minimal cost while being convenient to employ.
It is a further objective of this invention to provide for an ionizer which can be part of a filter and, if the filter is electronic with its own power supply, the ionizer can be connected to the filter's power supply. In this way, only one installation is required for one filter-ionizer combination.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.